Question

Please answer the question which is circled

Answer 1

If there is no friction between the surface and the ball then the rolling ball won't stop its course and it will roll to infinity.

There is no need of applying a continuous force, because friction as a force acts till the object is in motion and makes the object stop. When the

object stops friction is not acting upon it.

Trolley:
if we wish to keep an object in continuous motion we should apply a continuous force otherwise it stops it's motion by the action of friction.
So there should be continuous applied force that opposes friction and allow the body to move continuosly
In this case friction opposes the motion so to overcome the friction we have to apply the force continuously in order to keep trolley in a continuous motion

Answer 2

Yes, no continuous force has to be applied for continuous motion of an object.Because, all the planets are rotating as well as revolving around the Sun, so their motion is not due to the continuous force applied on them.

Rather they are in a continuous and uniform motion.And according to Newton's 1st law, "uniform motion is also the natural state of an object".

As far as the pushing of a trolley in a grocery is concerned, we need to supply a force to keep it moving because there is a friction provided by the ground as well as there can also be resistance provided by air which resist its continuous motion.And this is also in accordance with the Newton's 3rd law of motion.